Stents are known in the art. They are typically formed of a cylindrical metal mesh which can expand when pressure is internally applied. Alternatively, they can be formed of wire wrapped into a cylindrical shape.
As described in U.S. Pat. No. 4,776,337 to Palmaz, the cylindrical metal mesh shape is produced by laser cutting a thin walled metal tube. The laser cuts away all but the lines and curves of the mesh.
The method of U.S. '337 is applicable for relatively large mesh shapes and for meshes whose lines are relatively wide. However, for more delicate and/or intricate shapes, the spot size of the laser is too large.
Stents have been coated with various compounds and therapeutic agents to enhance their effectiveness. Stent coatings may be designed, for example, to be coated with a drug to facilitate the acceptance of the stent into a blood vessel lumen or to facilitate the delivery of therapeutic agents to a target site within a blood vessel. Such drug coated stents have been used in recent years to attempt to reduce the occurrence of restenosis. During the manufacture of coated stents, care must be taken to ensure that the coating is uniformly applied to the stent surface.
Various methods have been employed to apply coatings to stents. For example, the cylindrical surface of a finished stent may be sprayed with a coating substance or a spinning cylindrical stent may be dipped into a coating solution to achieve the desired coating.
U.S. Pat. No. 6,984,411 to Palasis et al. describes a method for applying a coating to stents that are being rolled about their longitudinal axis, where the stents are loaded onto rotating holders affixed to a conveyor, and the conveyor carries the rotating stents and holders through a coating applicator one or more times.
A disadvantage of these prior stent coating processes is that uniformity of stent coating is difficult to achieve when spraying the cylindrical surface of a finished stent. These prior stent coating processes also do not allow for the differential treatment of the luminal side of the stent and the vessel wall side of the stent.
A further disadvantage of currently available coating methods of stents is that the coating is made on both the luminal side and vessel wall side of the stent. Not having the ability to provide differential treatment of the luminal and vessel sides of the stent may limit potential applications of the coated stent.
A further disadvantage is that the desired ratio between coating on both surfaces, whether equal or not, is hard or impossible to control. A further disadvantage of existing processes is their inherent slow pace that limits capacity and cost efficiency.
Thus, there remains a need in the art to have a process of uniformly coating stents and providing a coating having differential treatment of the luminal side of the stent and the vessel wall side of the stent. It is also desirable for such process to be substantially faster and more cost efficient.